Control apparatus for a continuous cast billet



F. w. RYS 3,344,841

CONTROL APPARATUS FOR A CONTINUOUS CAST BILLET Oct. 3, 1967 Filed June 18, 1965 INVENTOR.

' FEEDR/CK W 2Y5 BY 4. (g Q United States Patent 3,344,841 CONTROL APPARATUS FOR A CONTINUOUS CAST BILLET Fredrick W. Rys, Pittsburgh, Pa., assignor to Koppers Company, Inc., a corporation of Delaware Filed June 18, 1965, Ser. No. 465,089 Claims. (Cl. 164-150) This invention relates to continuous metal casting and more particularly to improvements in apparatus to control the loop of a continuously cast billet.

In the continuous casting of metals, and of steel in particular, molten metal flows from a ladle into a tundish and then into a vertical casting mold which is usually vibrated or reciprocated vertically so as to prevent the casting from sticking to the walls of the mold. At the beginning of the casting operation, the bottom of the mold is closed temporarily by a dummy bar to which a casting adheres. Thereafter, the dummy bar is withdrawn and with it the casting is withdrawn from the mold. By the time the casting or billet emerges from the bottom of the mold, the skin or outer surface of the billet is thick enough to resist the internal pressure of the metal above it, and deformation by the conventional apron structure upon which the casting is supported. The dummy bar passes through a set of pinch rolls by means of which it and the casting are withdrawn from the mold.

After the cast strand Or billet passes through the pinch rolls, the billet is detached from the dummy bar and the billet is curved in an arcuate manner toward and through a set of entry or straightener rolls, disposed at a lower level below the pinch rolls.

The speed of the pinch rolls controls the rate of withdrawing the casting from the mold. The rate of withdrawing of the cast billet is correlated with the rate of pouring of the metal to maintain a predetermined liquid level in the mold. In order to more accurately control the liquid level in the mold, a conventional type of liquid level detecting device may be used, or any other suitable apparatus.

It is desirable to maintain the speed of the straightener rolls in synchronism with the speed of the pinch rolls so that the billet will assume a loop having a predetermined, substantially uniform configuration, which is generally an arc of a circle. Maintaining an are having a desired radius is difiicult, and a real danger is present because, if the loop should become too tight (or small) the billet may develop cracks and fissures, and may even break.

The pinch rolls squeeze the casting slightly as it passes therethrough so the dimensions change and the billet that exits from the pinch rolls is longer than the billet that entered the pinch rolls. Accordingly, the speed of the straightener rolls normally must be slightly faster than the speed of the pinch rolls. Many factors influence the speed relationship between the straightener rolls and the pinch rolls: typical of such factors are: changes in liquid level in the mold; changes in fluid flow due to the mold level and the flow characteristics of the molten metal; changes in length of the metal billet due to cooling of the metal; and the like. Nevertheless, a definite speed relation exists between the straightener rolls and the pinch rolls at any instant to provide the desired arc of the loop and this is considered synchronism for the purpose of this application.

Accordingly, the present invention is characterized by a continuous casting machine wherein there is synchronism between the pinch rolls and the straightener rolls and a continuous billet is withdrawn from a mold by pinch rolls and is thereafter curved so as to enter straightener rolls, which straighten the casting and then discharge it in a substantially horizontal direction by way of a sensor which contacts and senses the shape of the arc of the billet loop between the pinch and straightener rolls and controls the straightener rolls to maintain the are at a desired radius. In one embodiment, the invention includes a lever which is pivotally mounted adjacent the loop of the casting. One end of the lever is in continuous sliding contact with the periphery of the casting to con trol the speed of the straightener rolls so that, should the arcuate shape of the loop of the billet that is being continuously cast change because of non-synchronism between the pinch rolls and the straightener rolls, for example, the contacting lever pivots and electrically actuates the speed control unit. Whereupon, the speed of the straightener rolls is regulated according to the change in shape of the loop, whereby the loop of the continuous casting returns to its preselected initial configuration, and the straightener rolls are resynchronized with the pinch rolls.

For a further understanding of the present invention and for further advantages and features thereof reference may be made to the following description taken in con junction with the accompanying drawings which show for the purpose of exemplification a preferred embodiment of the invention.

The drawing is a schematic elevational view of one embodiment of the present invention including a schematic electrical control diagram.

A typical continuous casting apparatus 11, as illustrated in the drawing, includes a tundish 13 from which a continuous stream of molten metal 15 flows into the open or upper end of a Water-cooled mold 17. The molten metal forms a cast strand 19 within the mold, and the strand or billet is continuously withdrawn from the other end of the mold. A conventional dummy bar (not shown) or like apparatus is used to start the billet in the manner described previously.

The cast billet or strand 19, as it is withdrawn from the mold, is received by a conventional roller apron structure 21, disposed just below the bottom of the mold. The outer surfaces or skin of the strand or billet 19 are cooled by water emitted from the usual spray nozzles 23 located conveniently between adjacent sets of rollers in the apron structure 21. The continuous withdrawal of the strand 19 may be accomplished in any suitable manner. As illustrated herein, the strand 19 is being withdrawn by pinch rolls 25 which are powered by an electric 7 motor 27.

At a convenient level below the pinch rolls 25, the billet 19 passes between the rolls of a convenient straightener roll device 29, that is illustrated herein as comprising the usual upper 31 and lower rolls 33 respectively; Usually the straightener device 29 is laterally displaced away from the pinch roll vertical axis, as shown in the drawing, and the billet or strand 19 extends in an arcuate form or loop between the pinch rolls 25 and the straightener rolls 29. The straightener device 29 is also powered by an electric motor 35 in the usual manner.

In conventional installations, the motor 27, which drives the pinch rolls 25, determines the rate of withdrawal of a casting, and the speed of the pinch roll motor is governed in accordance with the level of molten metal in the mold by a conventional liquid metal level control devlce 28. One type of such a device is a gamma ray liquid level detecting device that usually includes a pair of spaced apart gamma ray detectors which are trained on the mold and which move upwardly and downwardly with the mold to detect variations in the level of the molten metal in the mold and electronically control the rate of pouring of the molten metal into the mold. Thus, the speed of the pinch rolls and the rate of withdrawal of the casting are directly influenced by the rate of pouring of molten metal .into the mold. r

The equipment described in the foregoing is conventional. The billet or strand 19 assumes a loop in the form of an arc of a circle (usually a quadrantal arc) extending from the exit side of the pinch rolls 25 to the entrance side of the straightener rolls 29. A typical loop may have a radius of 16 feet, but, of course, the loop radius may vary with the particular installation, and each particular continuous casting machine is adapted to produce arcuate billets having their own respective normal radius of curvature.

It is generally desirable to maintain the radius of the loop at some preselected value, say 16 feet. When the radius of curvature of the loop increases, the billet is said to assume a tight loop configuration; likewise, when the radius of curvature of the loop decreases, the billet is said to assume a slack loop configuration.

To overcome a slack loop or a tight loop condition, it has been necessary heretofore for the casting machine operating personnel to manually adjust from time to time, the speed of the straightener device to more nearly synchronize its speed with the speed of the pinch rolls. The casting machine operator was, therefore, required to keep practically a constant vigil lest the casting loop became either too tight or too slack. The operator attempted to manually adjust the speed of the straightener rolls so that there was substantial synchronism with the pinch rolls. However, since there are many factors, mentioned previously, which influence the casting rate, it has been almost impossible for the operator to maintain synchronism between the straightener rolls and the pinch rolls.

The present invention, however, readily and effectively solves the synchronizing problem by automatically con- "trolling the speed of the straightener rolls, as a function of right end as shown in the drawing, is maintained in reasonably light continuous'frictional sliding contact with the outer peripheral surface of the strand 19. A counterweight 51, which may be fixed to the other end of the 'lever 43a in a suitable manner, as by welding, is a simple device to maintain the lever 43a in pivoted sliding contact with the surface of the billet 19.

Adjacent the counterweight 51, a clevis 53 is fixed to Y the underside of the lever 43a, about where shown, and one end of a connecting rod 54 is pivotally pin-connected to the clevis 53, whose other end is suitably secured to one end of a length of roller chain 55.

At a suitable level below the lever 43a, there is provided another support structure including a horizontal platform 59 on which is mounted a conventional electrical signal generating device 61, indicated herein as a 1 differential transformer 60 having a movable core 62. The 'signal output of the transformer is applied across a potentiometer 39, and varies with the displacement of the core 62 from a null or central position. The signal generating device 61 is provided with an operative sprocket wheel 63, and a length of the roller chain 55 is threaded on the lower portion of the sprocket wheel 63 in such a manner that it passes around it and up and over an idler sprocket wheel 65; the sprocket wheel being suitably mounted on the platform 59.

The free end of roller chain 55 depends from the idler sprocket wheel 65 within a hollow tubular guide member 67, which is fixedly mounted to depend beneath the platform 59. The tubular guide member 67 is preferably closed at its bottom end by means of a bolted cap plate 69.

Within the tubular guide member 67, and suitably secured to the free end of the depending roller chain 55, there is a cylindrical counterweight 71. An arm 73, which is fixed to the counterweight, extends outwardly through an elongate longitudinal slot 74 in the wall of the tubular member 67 and terminates in shoe 75. The shoe 75 coacts with a pair of electrical switches 77, 79 that are mounted in spaced apart vertical relation on the support structure 59. Thus, as the sprocket 63 turns and the counterweight 71 rises and falls in the tubular guide member 67, the shoe 75 engages and trips switches 77 and 79 respectively.

Referring to the drawing, whenever the loop of the billet 19 changes from its normal quadrantal arcuate loop configuration, the lever 43a pivots responsively about the pivot mounting 45a as the counterweight 51 maintains the end 49a of the lever 43a in continuous sliding contact with the loop, regardless of the loop configuration. When the lOOp tends to slacken, for example, the end 49a pivots clockwise about the pivot mounting 45a, the roller chain 55 rotates the sprocket wheel 63 counterclockwise, and

the counterweight 71 rises in the guide tube 67. Rotation of the sprocket wheel 63 moves the core 62 with respect to the central position of the transformer winding, and

develops an electrical signal. Preferably, the transformer 69 is so constructed that it has a null or zero output when the'core is in its normal central position. Also, the transformer 60 has a small no-output or dead zone on either side of the zero position; a positive output signal when the core is on one side of the dead zone and a negative output on the other side.

As illustrated in the drawing, the motor 35 is controlled from a conventional servo amplifier 36 in accordance with signals from a signal chain comprising: signals across the potentiometer 37 from a tachometer 38 driven by the motor 35; the signal across the potentiometer 39 from the signaldeveloping dilferential transformer 60; and selectively either from the potentiometer 41, which receives the output from a tachometer 42 connected to the motor 27, or from the potentiometer 43'which receives a reference signal from a suitable source. The size of the signal from source 43, and consequently the speed of the motor 35,

.is controlled by the position of the wiper 44 which is manually positioned by control knob 45. Depending upon the position of arm 46, the motor 35 is selectively controlled by the motor 27 or by the reference source 43. The tachometer 42 is connected mechanically, in a conventional manner, with motor 27.

Now then, as the speed of the motor 27 increases, signal across potentiometer 41 increases, and, consequently the signal to amplifier 36 is greater. correspondingly, the speed of motor 35 is greater until such time as the signal from tachometer 38 cancels out the signal from tachometer 42. The relationship of the speed of the motor 35 to the speed of the motor 27 can be readily adjusted by moveter 38 cancels the reference signal. In either case, however, whether the motor 35 is following motor 27 or whether the motor 35 is being driven at a preset rate, the speed of the motor 35, in accordance with this invention,

is corrected as a function of the shape of the loop of the billet 19, and the arc of this loop is maintained constant. To this end, a corrective signal is developed across potentiometer 39 corresponding to the deviation of the arc of the loop of billet 19 from a predetermined set arcuate configuration.

Whenever the loop deviates from its normal or prescribed arc during the casting operation, the feeler arm 43a responds to the deviation and pivots about the pivot mount 45a. Consequently, the roller chain 55 rotates the sprocket wheel 63, and the output signal of the transformer 60 is changed. The change in signal output either adds to or subtracts from the reference signal being supplied by either the motor 27 (by way of tachometer 42) or the signal generator 43, and the increase or decrease in signal output either increases or decreases the speed of the straightener motor 35, so that the loop is brought back to its normal configuration.

If, for example, the straightener rolls are operating too fast in relation to synchronism with the pinch rolls, the loop configuration would become tight. The output signal from the signal developing device 43 would be negative and the speed of the straightener rolls motor 35 would be decreased. Thereafter, the loop would tend to slacken, and the loop would return to its normal configuration.

It was mentioned previously that the speed of the straightener motor, when synchronized with the pinch rolls, is slightly faster than the speed of the pinch rolls. The straightener rolls speed adjustment unit 45, 50 provides for manual adjustment of the speed of the straightener rolls advantageously within the limits of minus percent and plus 25 percent of the speed of the pinch rolls.

When the machine is placed in operation, and after the billet 19 commences to emerge from the pinch rolls, the upper roll 31 of the straightener rolls is raised to allow the billet 19 to enter between the rolls 31, 33. When the top roll 31 is raised, it opens an entry roll limit switch 87 (the open position being indicated by dotted lines in the drawing).

After the billet 19 enters the straightener 29, the top roll 31 is lowered in the usual manner and the entry roll limit switch 87 closes (shown in the drawing by the solid line form). Both of the limit switches 77, 79 are normally open. The upper limit switch 77 is connected to an electrical power supply bus 101 through a relay, R2. The lower limit switch 79 is also connected to the bus 101, and is connected in series with the entry roll limit switch 87 and a relay, R1.

In parallel with the top level limit switch 79 is an alarm horn 103 and contactor R1-3 of the relay R1. Paralleling contactor R1-3 is another contactor 'R2-1 of the relay R2.

Now, should'the loop deviate from its normal configuration and assume a tight loop condition, the feeler arm or lever 43a would pivot counterclockwise about the pivot point 45a, and the shoe 75 would actuate the lower limit switch 79 and close it. Relay R1 would then be energized and its contact R1-1 would open, whereupon the contactor M1 is de-energized. The de-energization of the contactor M1 opens it contactor M1 1 in the circuit to the straightener motor 35, wherefore the straightener 29 stops. At the same time, contactor R1-3 in the alarm horn circuit closes and the alarm horn 103 sounds.

Even though the straightener rolls at this moment are stopped, the pinch rolls, however, do not stop. The billet 19 continues to issue from the pinch rolls and the loop tends to slacken and return to its normal configuration. As the loop commences to slacken, the feeler arm 43a pivots responsively clockwise, and the counterweight 71 rises in the guide member 67. The arm 73 and shoe 75 likewise rise and disengage from the lower limit switch 79, opening the same. Relay R1 is again de-energized and the contactor M1 is energized, closing the contactor Ml-l. When contactor M1-1 closes, current againflows' to the 6 straightener motor 35 and it starts the straightener rolls 29 and moves the billet 19 through the machine 11.

If, instead of a tight loop condition, there is a slack loop condition, the feeler arm 43a pivots clockwise about the pivot 45a and the arm 73 raises the shoe 75 until it engages and closes the upper limit switch 77. Whereupon, the relay R1 is energized, its contactor R1-1 closes, and the alarm horn 103 sounds.

When the alarm horn sounds with the loop in the slack condition, the operating personnel are alerted and they can then revert to manual operation of the casting machine until the cause of the slack loop condition has been rectified.

There is also provided in the schematic circuit diagram a horn-silencing arrangement comprising a manual push button-silencing arrangement comprising a manual push button 105 and associated relays and contactors. Assuming that the horn 103 is sounding as a result of either a tight loop or a slack loop configuration. The machine operator first manually pushes the butt-on 105, whereby the relay R3 energizes and seals itself in through the closure of its contactor R3-1. It should be noted that in a respective loop condition, contactor R1-2 or contactor R2-2 will have closed previously when either relays R1 or R2 were energized, as explained previously. Thus, the effect of the manual operation of the push button 105 is that it silences the horn 103.

It is desirable for several reasons to provide manual silencing of the alarm horn. Firstly, the operating personnel of the casting machine are alerted to the malfunctioning of the machine; secondly, they manually actuate the push button 105 to silence the horn; and, lastly, if necessary they are required to manually operate the machine and rectify the conditions that cause the alarm to sound.

Typically, the feeler arm is maintained in contact with the billet at all times; deviations from the preselected loop configuartion are sensed by the feeler arm, whereupon the signal generator operates in the manner described herein to maintain synchronism between the straightener and the pinch rolls.

It will be noticed by referring to the drawing that a dead stop 107 is provided adjacent the pivotal mounting 45a. This is for the purpose of restricting the counterclockwise travel of the lever 43a and preventing the counterweight 71 from striking and possibly damaging the bolted cap plate 69. For example, when the loop approaches an'extremely tight configuration, the lever 43a will have pivoted in a counterclockwise direction until the counterweight 71 is almost at the bottom of the tubular guide member 67. At the same time, the shoe 75 is just contacting the lower switch and the lever is just about to engage the dead stop. As mentioned previously, when the lower limit switch 79 is actuated and closed, the straightener rolls stop. The pinch rolls, however, continue to Withdraw the casting and consequently theloop returns to its normal configuration. After a preselected time delay, the straightener rolls resume operation, and they are then resynchronized with the pinch rolls.

In another aspect of the invention, the sensor or feeler arm 43a may be replaced by a suitable type of sensor which is not in physical contact with the billet, such as photoelectric cell, gamma ray, or other radiation attenuation sensors. Each such sensor arrangements, of destrand or billet. Such a loop control mechanism may be an integral part of a continuous casting machine, and as such eliminates the necessity for operating personnel to constantly adjust the speed of the straightener in order to maintain synchronization between the straightener and the pinch rolls. Moreover, the apparatus of the present invention'is more efiective in controlling'the loop and maintaining synchronization between the straightener and the pinch rolls than the heretofore conventional manual control method.

Although the foregoing describes with a certain degree of particularity, a'preferred embodiment of the invention by way of an example, it is understood that the invention is not so limited, but is defined by what is hereinafter claimed.

I claim:

1. A continuous casting machine comprising:

(a) a mold wherein a strand of cast metal is formed from molten metal poured thereinto;

(b) powered pinch rolls disposed beneath said mold continuously engaging and withdrawing said strand;

(c) powered straightener rolls disposed beneath said pinch rolls continuously engaging said strand which extends in a loop between the pinch and straightener rolls;

((1) a first support adjacent said strand;

(e) a lever pivotally mounted to said first support with one end contacting the periphery of said looped strand; 7

(f) means maintaining said lever in continuing contact with said strand;

(g) signal developing device mounted adjacent said first support and operatively connected to said straightener rolls to vary the speed thereof; and

(b) means operatively connecting said signal developing device to said lever whereby, when the speed of the straightener and pinch rolls becomes non-synchronous and the configuration of said loop changes, said signal developing device is actuated in response to the movement of said lever whereby the speed of said straightener rolls is changed and resynchronized with said pinch rolls.

2. The invention set forth in claim 1 wherein:

(a) the means operatively connecting said lever to said signal developing device is provided with switch actuating means; and

(b) an electrical switch is disposed adjacent said switch actuating means and operatively connected to said powered straightener rolls whereby, when the speeds of the straightener rolls exceeds the speed of the pinch rolls, said switch actuating means actuates said switch and said straightener rolls stop.

3. The invention set forth in claim 2 wherein:

(a) as said loop tends to slacken after the speed of said straightener rolls stops, said switch becomes disengaged from said switch actuating means; and

(b) means is provided for restarting said straightener rolls and resynchronizing the same with said pinch rolls. 7

4. In a continuous casting machine wherein a cast strand extends in a loop between separately powered pinch rolls and straightener rolls, the improvement comprising:

(a) *means continuously engaging said strand which is responsive to changes in the shape of said loop;

(b) means for regulating the speed of said straightener rollspand ('0) means connecting said strand engagingme'ans and said straightener rolls speed regulating means whereby when said straightener rolls become non-synchronized with said pinch rolls and the contour of said loop changes, said strand engaging means actuates said straightener rrolls speed regulating means and the speed of the straightener rolls is resynchronized with the pinch rolls. 7

.5. In a continuous casting machine wherein a cast strand extends in a loop between electric motor powered pinch rolls and electric motor powered straightener rolls,

the improvement comprising:

(a) a support adjacent said arcuate strand;

(b) a feeler arm pivotally mounted to said support with one end thereof contacting the periphery of said strand; 7

(c) means maintaining said feeler arm in continuous contact with said strand;

(d) a supply of electric power;

(e) a signal developing device mounted adjacent said feeler arm and connected to said power supply;

(f a reference signal generated by said powered pinch rolls; and

(g) -means operatively connecting said signal develop- 7 ing device to said feeler arm whereby when said loop deviates from a preselected form, the said lever responsively actuates said signal developing device and the output of said signal developing device is added to or subtracted from the reference signal and the speed of the straightener motor is increased or decreased until said straightener is synchronized with said pinch rolls.

6. The invention set forth in claim 5 wherein:

(a) a potentiometer is connected to the straightener motor whereby the speed of said motor may be varied within the range of minus ten percent and plilrs twenty-five percent of the speed of the pinch ro ls.

7. The invention set forth in claim 6 wherein:

(a) a limit switch is mounted to said support adjacent said signal developing device;

(b) a normally energized contactor is connected to said source of power and in the circuit carrying power to said straightener motor; and

(c) means is provided to actuate said switch when said signal developing device operates beyond a preselected point and said limit switch is closed and said contactor is de-energized whereby power to said straightener motor is interrupted and said straightener stops.

8. In a continuous casting machine wherein a cast strand extends in a loop between electric motor powered pinch rolls and electric poweredrstraightener rolls, the improvement comprising:

a first support adjacent said loop;

a feeler arm pivotally mounted to said first support with one end thereof in contact with said loop;

means maintaining said feeler arm in continuing contact with said loop;

a second support structure; 7

a signal developing device mounted to said second support structure;

means operatively connecting said feeler arm to said signal developing device whereby when said loop deviates from a predetermined configuration, said signal developing device operates responsively;

first and second spaced apart normally open switches mounted tosaid second support; I I

means connected to said feeler arm and engageable with said limit switches when the feeler arm pivots beyond a predetermined angular sector;

a source of electric power;

a transformer operatively connected to said source of power and to said signal developing device whereby the voltage at said vsignal developing device is less than the source voltage;

a normally energized first contactor connected in the circuit from the source of power to the straightener motor;

an alarm horn;

means connecting said born to the source of power through a normally open second contactor;

means connecting said normally energized first contactor to said source of power through a normally closed third contactor; and 7 means connecting the first normally open switch to the source of power through a first relay which actuates the normally closed third contactor whereby, when the loop deviates from its predetermined configuration and said feeler arm pivots responsivley enough to close said first normally open switch, said first relay is energized and said normally closed third contactor opens whereupon the normally energized first contactor is de-energized thereby opening the circuit between the generator and the straightener motor and said straightener stops, and at the same time said normally open second contactor closes and said alarm horn sounds. 9. The invention set forth in claim 8 including: (a) means to restart said straightener comprising (1) means to reopen the closed first normally open switch after said loop has changed its configuration, whereby said first relay is de-energized and said first contactor is energized and current flow in the circuit between said generator and said straightener rolls is resumed and the straightener motor starts. 10. The invention set forth in claim 9 including: (a) means connecting said horn to the source of power through a normally open fourth relay; and (b) means connecting the second normally open switch to the source of power through a second relay which actuates the normally open fourth relay whereby when the loop deviates from its predetermined configuration and said feeler arm pivots responsively enough to close said second normally open switch, said second relay is energized and the fourth contactor closes and the horn sounds an alarm. 11. The invention set forth in claim 10 including means to silence the alarm horn when the same sounds comprising:

12. The invention set forth in claim 10 including means to silence the alarm horn when the same sounds comprising:

(a) a push button switch connected to said source of power through a third relay; (b) a fifth contactor connected in parallel with said push button switch across said power source; and (c) a seventh contactor connected in series with said third relay whereby when said push button switch is actuated closed said third relay is energized and said fifth contactor closes, said seventh contactor being closed when said second relay is energized.

13. A continuous casting machine comprising:

(a) a casting mold;

(b) pinch rolls for withdrawing continuously a cast strand from said mold;

(c) straightener rolls for straightening said cast strand;

(d) means for driving said straightener rolls at a speed proportional to the speed of said pinch rolls whereby said cast strand extends in an are from said pinch rolls to said straightener rolls; and

(e) means for changing the proportional speed relationship as a function of curvature of the arc of said cast strand.

14. A continuous casting machine comprising:

(a) a casting mold;

(b) powered means for withdrawing continuously a cast strand from said mold;

(c) powered straightener rolls for straightening said cast strand extending in a loop between said pinch rolls and said straightener rolls, the speed of said straightener rolls being proportional to the speed of said pinch rolls;

(d) 3 sensor continuously in contact with said loop;

(e) means actuated responsively to movement of said sensor for changing the speed of said straightener rolls in response to the change in the loop.

15. A continuous casting machine comprising:

(a) a casting mold;

(b) powered means for withdrawing continuously a cast strand of metal from said mold;

(c) powered straightener rolls for straightening said cast strand extending in a loop between said powered strand withdrawal means and said straightener rolls;

(d) a sensor in continuous contact with said loop; and

(e) signal developing means operatively connected to said sensor and said straightener rolls whereby as said sensor responds to changes in said loop the speed of said straightener rolls varies as a function of the shape of said loop.

16. A continuous casting machine comprising:

(a) a casting mold;

(b) powered means for withdrawing continuously a cast strand of metal from said mold;-

(c) powered straightener rolls for straightening said cast strand extending in a loop between said powered strand withdrawal means and said straightener rolls;

(d) sensor means adapted to detect changes in the shape of said loop;

(e) a sensor in continuous contact with said loop; and

(f) means for stopping said straightener rolls whenever the shape of said loop varies from a preselected range of shapes.

17. The invention set forth in claim 16 wherein:

(a) means is provided for restarting said straightener rolls.

18. A continuous casting machine comprising:

(a) a casting mold;

(b) powered means for withdrawing continuously a cast strand of metal from said mold;

(c) powered straightener rolls for straightening said cast strand extending in a loop between said powered strand withdrawal means and said straightener rolls;

(d) a sensor in continuous contact with said loop;

(e) a source of electric power;

(if) a signal developing device connected to said source of power;

(g) means connected to said signal developing device and to the straightener rolls power drive means; (h) operative means connecting said sensor to said signal developing device whereby when said loop changes shape said signal developing device correspondingly changes the speed of said straightener rolls power means.

19. A continuous casting machine comprising:

(a) a casting mold;

(b) powered means for withdrawing continuously a cast strand of metal from said mold;

(0) powered straightener rolls for straightening said cast strand extending in a loop between said powered strand withdrawal means and said straightener rolls;

(d) a support adjacent said arcuate strand;

(e) a feeler arm pivotally mounted to said support with one end thereof contacting the periphery of said strand;

(f) means maintaining said feeler arm in continuous contact with said strand;

(g) a supply of electric power;

(h) a signal developing device mounted adjacent said feeler arm and connected to said power supply; (i) a reference signal generated by said powered pinch rolls; and

(j) means operatively connecting said signal developing device to said feeler arm whereby when said loop deviates from a preselected form, the said lever responsively actuates said signal developing device and the output of said signal developing device is added to or subtracted from the reference signal I and the speed of the straightener motor is increased or decreased until said straightener is synchronized with said pinch rolls.

20. The invention set forth in claim 19 wherein:

(a) a potentiometer is connected to the straightener motor whereby the speed of said motor may be References Cited UNITED STATES PATENTS Schwarz.

Harter 164-282 Carleton 164150 Barnard et al. 164154 Krueger 164282 Thalrnann 164-282 varied .within the range of minus ten percent and 10 L SPENCER OVERHOLSER, Primary Examiner- R. S. ANNEAR, Assistant Examiner.

plus twenty-five percent of the speed of the pinch rolls. 

13. A CONTINUOUS CASTING MACHINE COMPRISING: (A) A CASTING MOLD; (B) PINCH ROLLS FOR WITHDRAWIBG CONTINUOUSLY A CAST STRAND FROM SAID MOLD; (C) STRAIGHTENER ROLLS FOR STRAIGHTENING SAID CAST STRAND; (D) MEANS FOR DRIVING SAID STRAIGHTENER ROLLS AT A SPEED PROPORTIONAL TO THE SPEED OF SAID PINCH ROLLS WHEREBY SAID CAST STRAND EXTENDS IN AN ARC FROM SAID PINCH ROLLS TO SAID STRAIGHTENER ROLLS; AND 